HVAC Applications of Valves

HVAC Valves are such components without which we cannot control flow in pipes .Valves are needed for every media whether it is water, gas, air or any other liquid. Valves would have been needed for solids if they could have ability to flow. Like other areas, valves find its extensive use in HVAC (heating, ventilation and air-conditioning).

With special focus on HVAC, following are the some major hvac application of valves.

• Water Chiller, the heart of HVAC system, has valves on inlet and outlet lines of chilled water and cooling water. These valves are usually gate and globe valves which are used for isolation and throttling purposes. Water chiller operates on vapor compression cycle or vapor absorption cycles which also require valves internally as a requirement of thermodynamics. For example Refrigerant expansion valve is needed inside a water chiller cycle. Chilled and cooling water headers also need valves for isolation and heating/cooling changeover.
• Similar to water chillers, HVAC hot water generator has also valves on its inlet and outlet for isolation and flow control purposes. If water chiller can also act as water heater then there is no need of hot water generator obviously.
• Chilled water pumps and cooling water pumps have also isolation and throttling valves on their inlets and outlets. When we talk about water pumps then there are also check valves at the outlet of pumps to prevent reverse flow.
• Cooling towers are another hvac equipments which require valves at inlet and outlet for flow control of cooling water. Sometimes a float valve is also in the basin of cooling tower to control the level of water in cooling streams. Valves would also be needed for make-up water lines in HVAC system and cooling towers.
• Air handling units (AHUs) also need valves at inlet and outlet to regulate chilled water as per demand of cooling in the spaces depending upon the type of HVACcontrol system. These air handling unit valves are also connected to some HVAC software to remotely operate them as per cooling/heating demand from HVAC users. Drain valves are also provisioned inside air handling units.
• If Fan Coil Units (FCUs) are installed in individual rooms then valves will also be installed at entry and exit of these units to have precise control of cooling /heating for occupants of that space.

Ball Valve How it Works

What is a Ball Valve ?

A ball valve is a rotational motion (quarter turn),quick rotating valve that uses a ball-shaped disk to stop or start or regulate fluid flow.The function of this type of valves,ball is same as of disk in globe valve. When the valve handle is turned to open the valve, the spherical ball rotates to a position where the hole through the ball is in-line with the valve body inlet and outlet of flow. When the valve is shut, the ball is rotated so  that the hole is perpendicular to the flow openings of the valve body and the flow is stopped. 

Ball valve actuators are of the quick-acting type, which require a 90° turn of the valve handle to operate the valve. Some ball valveactuators such as planetary gear-operated,  allow the use of a relatively small operating force to operate a fairly large valve.

Some ball type valves have been developed with a spherical surface coated plug that is off to one side in the open position and rotates into the flow passage until diskblocks the flow path completely. 

Advantages of Ball Valves

• A ball valve is the least expensive of any valve arrangement
• Ball valve offers low maintenance costs.
• Ball valves are compact, require no lubrication, and give tight sealing with low torque.

Disadvantages of Ball Valves

• Ball type valves(especially old designs) have relatively poor throttling characteristics.
• In a throttling position, the partially exposed seat of ball valve rapidly erodes because of the impingement of high velocity flow.

Ball valve

Valve Materials in Ball valves

Balls are usually metallic with trim (seats) produced from elastomeric (like rubber) materials. Plastic construction in ball valves is also available.

The resilient seats for ball valves are made from teflon (TFE), filled TFE, Nylon, Buna-N, Neoprene, other combinations of these materials.Because of these elastomeric materials ball valves cannot be traditionally used at elevated temperature and engineer must take care while selecting ball valve for particular application.

Ball Valve Port Patterns ,Bonnet & Stem Design

Ball valves are available in the venturi, reduced, and full port pattern. The full port

pattern has a ball with a bore equal to the inside diameter of the pipe.

The stem and ball connection is explained here.The stem in a ball valve is not fastened to the ball. It normally has a rectangular portion at the ball end which fits into a slot cut into the ball. The enlargement permits rotation of the ball as the stem is turned. A bonnet cap fastens to the body, which holds the stem assembly and ball in place. Adjustment of the bonnet cap permits compression of the packing, which supplies the stem seal. Packing for ball valvestems is usually in the configuration of die-formed packing rings normally of TFE, TFE-filled, or TFE-impregnated material. Some ball valve stems are sealed by means of O-rings rather than packing.

Ball Valve Positions

Some ball valves are equipped with stops that permit only 90° rotation. Others do not have stops and may be rotated 360°. Whether there is stop available or not, a 90° rotation is all that is required for closing or opening a ball valve.

The handle indicates valve ball position. When the handle lies along the axis of the valve, the valve is open. When the handle lies 90° across the axis of the valve, the valve is closed. Some ball valve stems have a groove cut in the top face of the stem that shows the flowpath through the ball. Observation of the groove position indicates the position of the port through the ball. This feature is particularly advantageous on multiport ball valves.

HVAC Types of Chillers

Chiller Types have been designed to cater to the diversified requirement of industrial chillers.Water chillers have evolved due to the variety in availability of type of energy at industry or small level.Types of chillers have made the use of the chillers flexible in terms of energy input.

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Water chillers

Industrial research in the field of chiller has eased the selection of chillers in an economical and robust manner.There is no need of worry whatever type of energy you have available with you.

Each type of chiller targets the specific users classified on the basis of type of energy they have.

HVAC systems employ different types of chillers within the available resources of clients or users.

A chiller may be the best option for particular application while the same chiller may costly or less feasible for another application or plant.

Hvac water chillers are classified primarily on the basis of cycle on which they work.

• Vapor compression chillers or compression chillers or electric chillers
• Vapor absorption chillers or absorption chillers or ammonia chillers or lithium bromide chillers

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HVAC chiller types

Vapor compression chillers are further classified on following basis.

• Type of compressor i.e reciprocating compressor,rotory compressor or screw compressor type vapor compressor chillers
• Type of condenser i.e air cooled condenser or air cooled chillers OR water cooled condensers or water cooled chillers

While Vapor absorption chillers are further classified as following:

• Direct fired absorption chillers (Natural gas, Diesel or Kerosene Oil Operated)
• Indirect fired absorption chillers

  
  

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Gate Valve

Gate Valve

What is a Gate Valve

A gate valve is a linear motion valve used to start or stop fluid flow. The name gate is derived from the appearance of the disk in the flow stream. 

Gate valve Diagram

The disk of a gate valve is completely removed from the flow stream when the valve is fully open.When the valve is fully closed, a disk-to-seal ring contact surface exists for 360 degree.With the proper mating of a disk to the seal ring, very little or no leakage occurs across the disk when the gate valve is closed.

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A gate valve can be used for a wide variety of fluids and provides a tight seal when closed.  

Major disadvantages  of a gate valve

• It is not suitable for throttling applications.
• It is prone to vibration in the partially open  state. 
• It is more subject to seat and disk wear than a globe valve.
• Repairs, such as lapping and grinding, are generally more difficult to accomplish.

Disk Design of Gate Valve

Gate valves are available with a variety of disks. Classification of gate valves is usually made by the type disk used: 

• solid wedge
• flexible wedge
• split wedge
• parallel disk

Solid wedges, flexible wedges, and split wedges are used in valves having inclined seats. Parallel disks are used in valves having parallel seats.

Gate valve

Regardless of the style of wedge or disk used, the disk is usually replaceable. In services where solids or high velocity may cause rapid erosion of the seat or disk, these components should have a high surface hardness and should have replacement seats as well as disks. If the seats are not replaceable, seat damage requires removal of the valve from the line for refacing of the seat, or refacing of the seat in place. Valves being used in corrosion service should normally be specified with replaceable seats.

Gate Valve Stem Design

Gate valves are classified as either rising stem or non rising stem valves. For the non rising stem gate valve, the stem is threaded on the lower end into the gate. As the hand wheel on the stem is rotated, the gate travels up or down the stem on the threads while the stem remains vertically stationary. This type of valve will almost always have a pointer-type indicator threaded onto the upper end of the stem to indicate valve position. 

The non rising stem configuration places the stem threads within the boundary established by the valve packing out of contact with the environment. This configuration assures that the stem merely rotates in the packing without much danger of carrying dirt into the packing from outside to inside.

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Rising stem gate valves are designed so that the stem is raised out of the flow path when the valve is open. Rising stem gate valves come in two basic designs. Some valves have a stem that rises through the hand wheel while others have a stem that is threaded to the bonnet.

Gate Valve Seat Design

Seats for gate valves are either provided integral with the valve body or in a seat ring type of construction. Seat ring construction provides seats which are either threaded into position or are pressed into position and seal welded to the valve body. The latter form of construction is recommended for higher temperature service.

Integral seats provide a seat of the same material of construction as the valve body while the pressed-in or threaded-in seats permit variation. Rings with hard facings may be supplied for the application where they are required.

Small, forged steel, gate valves may have hard faced seats pressed into the body.In some series, this type of valve in sizes from 1/2 to 2 inches is rated for 2500 psig steam service. In large gate valves, disks are often of the solid wedge type with seat rings threaded in, welded in, or pressed in. Screwed in seat rings are considered replaceable since they may be removed and replaced.